Increase in Number of U.S. Syphilis Cases Primarily Due to Immunity Changes, Not Sexual Practices, Study Says
The long-term dynamics of human immunity to syphilis infection have played a "major" role in the recent increase in the number of syphilis cases in the United States, indicating that health officials' concerns that the rise was occurring primarily due to unsafe sex practices among men who have sex with men likely are unsubstantiated, according to a study published in the Jan. 27 issue of the journal Nature, AFP/TurkishPress.com reports (AFP/TurkishPress.com, 1/26). According to CDC's "2003 STD Surveillance Report," which was released in November 2004, the number of reported primary and secondary syphilis cases in the United States increased from 6,862 cases in 2002 to 7,177 cases in 2003. In addition, CDC estimates that about 60% of syphilis cases in the United States occur among men who have unprotected sex with men. The increase in the number of syphilis cases among MSM was of "particular concern" to officials because as many as 70% of MSM who recently have been diagnosed with syphilis also are HIV-positive (Kaiser Daily HIV/AIDS Report, 11/30/04).
Dr. Nicholas Grassly, an infectious disease epidemiologist, and colleagues from the Imperial College of London studied CDC data on syphilis and gonorrhea cases from 68 U.S. cities collected from 1941 to 2002, Reuters reports (Reaney, Reuters, 1/26). The researchers found an oscillating pattern of higher and lower numbers of syphilis cases that repeated in eight-to 11-year cycles, but no such pattern existed for gonorrhea cases (Crenson, AP/Columbia State, 1/27). According to CDC data, syphilis cases declined by about 89% between 1990 and 2000, but the number of cases rose from 5,972 in 2000 to 6,103 in 2001, which was the first increase since 1990. The researchers also noted that syphilis epidemics began in cities across the country at the same time and became "more synchronized" over time, according to Reuters. "Syphilis shows these repeated epidemics every 10 years, but gonorrhea does not. You would expect them to be very much the same given they are spread by the same route, they tend to infect the same people, they last the same length of time and are treatable by antibiotics," Grassly said, adding, "When there is an outbreak of syphilis, one should not immediately say people are adopting unsafe sexual practices. It is actually the fact that syphilis generates protective immunity that drives these epidemics" (Reuters, 1/26). "As well as analyzing previous epidemics, it may also be possible to use these findings to help doctors and sexual health workers predict and prepare for future outbreaks of the disease," Grassly said, adding that "[t]roughs" in the number of syphilis cases "offer an unprecedented opportunity for eradication of the disease. However, when this opportunity is missed, an epidemic is likely to follow" (Reuters Health, 1/26).